This invention relates to a ball-point pen tip and a ball-point pen provided with the same, and more particularly, to a type thereof which uses an aqueous solution based low viscosity ink.
According to the conventional ball-point pen, a tip portion includes a socket formed of plastic material or metal such as brass and nickel silver, and a steel or rubby-ball rotatably disposed in the tip portion of the socket. Further, an ink guide stem is inserted in the rear portion of the socket, and an ink passage is formed between a ball seat and the ink guide stem.
In this type of the pen tip, the socket must stably hold the ball, even when large writing force is applied to the pen tip. Further, in order to provide confortable writing for long duration, the ball seat must sustain frictional wear due to the rotational surface contact with the rigid ball. Furthermore, ink must be constantly supplied into the ball seat and the ink passage in conformity with the consumption amount of the ink, so that the ink passage must provide sufficient cross-sectional area so as to permit the ink to pass therethrough and must create capillary action for retaining the low viscosity ink therein so as to prevent the ball-point pen from failing to write or skipping.
In case the socket made of plastic material is used, it is possible to produce axial channels, as the ink passages, having complicated cross-sectional shape by molding in order to create sufficient capillary action. However, the ball seat is extremely worn due to rotational contact with the ball, to thus degrade writing performance for long duration. Further, the plastic socket does not provide sufficient force for holding the ball therein in comparison with the metal socket, so that ball may be accidentally released or disengaged from the ball seat during writing.
On the other hand, in case the socket made of metal is used, it would be difficult to produce a plurality of axial channels, as the ink passages, to create capillary action. Generally used are copper alloys such as brass and nickel silver those being easily subject to machining or cutting. However, it is yet difficult to produce axial capillary channels by machining, and resultant socket is costly with low productivity. Further, since brass and nickel silver are apt to be corroded by the aqueous solution ink, the ink to be used must be selected in light of its characteristics such as pH and Cl-ion content, resulting in reducing variety of the aqueous solution ink.
Another type of socket of ball-point pen is proposed in U.S. Pat. No. 3,781,123, wherein a central axial bore having simplified circular cross-section is formed instead of the plurality of axial channels for capillary action. The central bore has one end in communication with radial grooves each having capillary dimension and radially spreading in the surface of the ball seat. However, according to this type, in case the central bore has relatively large diameter so as to supply large amount of ink, reduced is the capillarity for maintaining capillary action of the aqueous solution based low viscosity ink, and therefore, such socket may not be appreciated as a ball-point pen tip which uses aqueous solution ink.